1. Field of the Invention
The present invention relates to a method and a device for cooling a rotary kiln having a cylindrical outer jacket.
2. Description Of Related Art
Rotary kilns with a cylindrical outer steel jacket and an inner ceramic lining are, for instance, used as cement kilns and lime sludge reburning kilns. They may also be employed for burning waste, e.g. hazardous waste. When a rotary kiln is used for combustion, the steel jacket and the lining are worn as a result of the high temperature in the kiln and the considerable variations in temperature that arise when the kiln rotates. In addition, both the steel jacket and the lining are mechanically worn as a result of the rotary motion, and the lining is also worn by chemical attack. In a rotary kiln employed for burning chemical waste, the lining and the steel jacket have to be replaced, wholly or partly, after about 6,000 and about 25,000 hours of operation, respectively. However, if the temperature of the jacket is reduced and maintained at a relatively constant level, the service life of both the jacket and the lining is much prolonged.
Efforts have therefore been made to cool rotary kilns. In prior-art methods, the jacket of the rotary kiln is cooled with the aid of water. Water-cooling is, however, extremely difficult to carry out in practice, since it requires an extremely water-tight enclosure of the kiln in order to make it possible to make use of the water steam or hot water formed upon the cooling, and also in order to protect the surroundings and the device which rotates the kiln. Naturally, water-cooling also involves problems of corrosion.